This invention relates generally to a new and improved pressure limiting valve for ventilation gas apparatus. More particularly, this invention relates to a new and improved adjustable pressure limiting valve for adjustably controlling the peak inspiratory pressure of ventilation gas with which a person, particularly an infant, is ventilated. Still more particularly, this invention relates to a new and improved pressure limiting valve for both adjustably controlling such peak inspiratory pressure and for providing a base line pressure for pressurized ventilation gas received by the apparatus from a source, and to which the person, particularly an infant, is exposed during periods between periods of inspiration.
As known to those skilled in the art, manual ventilation of infants with a ventilation gas such as compressed or pressurized oxygen is commonly indicated for resuscitation, for transport of ventilator-dependent infants, to increase the concentration of delivered ventilation gas and to oxygenate the infants prior to and after performing tracheobronchial suctioning.
A variety of reusable and disposable devices comprising ventilation gas apparatus are known to the art for manual ventilation of a person such as an infant. These apparatus can generally be categorized into two types: self-inflating or flow-dependent breathing bag apparatus. Regardless of the type, the primary problem or objective in ventilating infants is to control the pressure of the ventilation gas delivered to the infants. Infants are particularly challenging in this regard in that their lungs are more fragile than those of adults but less compliant, therefore, fine control of delivered peak inspiratory pressure of the ventilation gas delivered to an infant is critical. Furthermore, base line pressure, i.e. the pressure of the ventilation gas present in the ventilation gas apparatus and to which the lungs of the person being ventilated are exposed during periods between the periods the ventilation gas is delivered to the patient, i.e. periods between delivered breaths, must be controlled to prevent collapse or over-distension of the person's lungs, particularly those of an infant. Control of such base line pressure is particularly important for infants being ventilated because such control, it is believed, at least facilitates exhalation by the infant during the periods between the periods the infant is being ventilated or the periods between delivered breaths.
Numerous relatively complicated pressure limiting valves, and pressure limiting valve systems, are known to the art for controlling the peak inspiratory pressure of ventilation gas delivered to a person such as an infant during manual ventilation. In most instances, however, the delivered peak inspiratory pressure of-the ventilation gas by such prior art apparatus is largely dependent on operator technique in compressing or squeezing the breathing bag which, upon squeezing or compression, delivers the ventilation gas to the person through the-ventilation gas apparatus. The self-inflating breathing bag ventilation apparatus known to the art typically include a fixed pop-off valve as a safety back-up to prevent delivery to the infant of undesirably high or elevated inspiratory ventilation gas pressures, but such known valves and valve systems typically are not adjustable whereby the pressure of the delivered ventilation gas up to the level of the pop-off pressure of the fixed pop-off valve remains dependent upon the technique of the operator compressing the self-inflating breathing bag. Ventilation gas apparatus employing flow-dependent breathing bags typically incorporate a simple adjustable bleed valve having an adjustable orifice to control the exhaust pressure of the ventilating gas. This bleed valve has been found to be effective only to obtain an acceptable base line pressure at the flow rate of the ventilation gas into the ventilation gas apparatus. However, this type of ventilation gas apparatus is very flow-dependent whereby a small difference in operator technique of squeezing or depressing the flow-dependent breathing bag can significantly alter the delivered inspiratory pressure of the ventilation gas.
Also known to the art are reusable, adjustable metal pop-off valves which incorporate a spring and disc and which are also known for controlling the peak inspiratory pressure of ventilating gas delivered to a person such as an infant during ventilation, e.g. during resuscitation. These pop-off valves, which are generally known in the art as adjustable pressure limiting valves, apparently are at present the most effective in limiting the peak inspiratory pressure of ventilation gas delivered to .infants. However, because these pop-off valves only relieve pressure once the preset threshold is attained, an undesirable build-up of the ventilation gas in the apparatus, to which the person being exposed or subjected, is possible during periods between periods during which the person is being ventilated with the ventilation gas or during periods between delivered breaths. This condition is sometimes referred to in the art as elevated base line pressure or inadvertent PEEP (Positive End Expiratory Pressure). If such base line pressure becomes too high, particularly during the periods between the periods the infant is being ventilated, it is believed that the ability of the infant to exhale can be greatly impaired. Furthermore, these valves suffer from the disadvantages of other reusable devices in that they are expensive, they must be disassembled for cleaning between use and thereafter reassembled, and they must be periodically maintained.
Accordingly, there exists a need in the art for a new and improved pressure limiting valve for insertion into ventilation gas apparatus which can be mechanically or manually adjusted to provide control, particularly adjustable control, of the peak inspiratory pressure of the ventilation gas substantially independent of operator technique in compressing or squeezing the breathing bag. Further, there exists a need in the art for a new and improved adjustable pressure limiting valve for insertion into ventilation gas apparatus which provides or limits a base line pressure for the ventilation gas also substantially independent of the technique of the operator in squeezing or compressing the breathing bag. Still further there exists a need in the art for a new and improved adjustable pressure limiting valve which provides control of both such peak inspiratory ventilation gas pressure and such base line pressure.